1. Field of the Invention
The present invention relates to an apparatus and method of converting the format of an image signal, and more particularly, to an apparatus and method of converting a frame and/or field rate using different motion compensation methods according to motion information of each block of the frame/field.
2. Description of the Related Art
In general, in order to exchange TV programs complying with a variety of TV standards, a format conversion of the programs is needed. In the early stage of TV format conversion, the format conversion was performed using a repetition of a frame and a simple spatiotemporal filter, which caused visually annoying motion jitter and blurring at the edges of an image. In particular, when screen resolution is higher as in a high definition television (i.e. an HDTV), these phenomena are very significant. Recently, in order to remove the phenomena, frame conversion methods using motion compensation have been developed.
FIG. 1 is a conceptual diagram showing a method of converting a frame rate using a conventional compensation method. Referring to FIG. 1, a frame Fi({right arrow over (x)},n−½) to be interpolated is defined using a 3-tap median filtering as in the following equation 1:
                                          F            i                    ⁡                      (                                          x                →                            ,                              n                -                                                      1                    ′                                    2                                                      )                          =                  MEDIAN          ⁡                      (                          mcl              ,              av              ,              mcr                        )                                              (        1        )            
Here, data obtained from two neighboring frames (n−1, n) considering motion traces are “mcl” and “mcr,” data obtained by linear interpolation of the two frames is “av”. These data can be expressed as follows.
                                                        mcl              =                              F                ⁡                                  (                                                                                    x                        →                                            -                                              α                        ⁢                                                                                                  ⁢                                                                              D                            →                                                    ⁡                                                      (                                                                                          x                                →                                                            ,                              n                                                        )                                                                                                                ,                                          n                      -                      1                                                        )                                                                                                        mcr              =                              F                ⁡                                  (                                                                                    x                        →                                            -                                                                        (                                                      1                            -                            α                                                    )                                                ⁢                                                                              D                            →                                                    ⁡                                                      (                                                                                          x                                →                                                            ,                              n                                                        )                                                                                                                ,                    n                                    )                                                                                                        av              =                                                1                  2                                ⁢                                  (                                                            F                      ⁡                                              (                                                                              x                            →                                                    ,                          n                                                )                                                              +                                          F                      ⁡                                              (                                                                              x                            →                                                    ,                                                      n                            -                            1                                                                          )                                                                              )                                                                                        (        2        )            Here, α is determined by the time at which a frame to be interpolated from the two frames will be located, and {right arrow over (D)} is a motion vector.
If the motion vector {right arrow over (D)} is accurately estimated in Equation 2, the motion compensation data have the values of “mcl” and “mcr,” and the values are determined as the pixel to be interpolated. Presently, however, if the motion vector {right arrow over (D)} is not accurate, the motion compensation data have different values, and therefore it is highly probable to determine “av” data that do not consider motions as pixel to be interpolated. Since the conventional compensation-type interpolation method is performed in units of a frame/field block, if the estimated motion vector {right arrow over (D)} is not accurate, block artifacts occur.